Apparatus for and method of removing oxides from strip



Dgc. 2, 1958 E. c. MCHENRY 2,

APPARATUS FOR AND METHOD OF REMOVING OXIDES FROM STRIP Filed Dec. '5, 1956 Fig.|

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INYENTOR Ernest C. Mc Henry United States Patent APPARATUS FOR AND METHOD OF REMOVING OXIDES FROM STRIP Ernest C. McHenry, Leechburg, Pa., assignor to Allegheny Ludlum Steel Corporation, Brackenritlge, Pa., a corporation of Pennsylvania Application December 5, 1956, Serial No. 626,529 7 Claims. (Cl. 134-15) This invention relates to apparatus for, and the method of, removing oxides from the surface of strip material formed from refractory metals.

In producing strip material of refractory metal of the class of titanium, titanium base alloys, zirconium and zirconium base alloys, it is necessary in processing the metal into strip of commercial quality to remove oxides, scale and the like therefrom. Attempts have been made in the past to effectively remove the oxides from such metal strip by continuously passing the strip through a heated alkali metal caustic bath formed of molten salts such as the commercially available Virgo or Kolene salts and thereafter pickling the treated strip. While such procedure has been effective in the production of stainless steel strip, it has not proven to be successful in the cleaning of metal strip formed of refractory metal of the class of titanium, titanium base alloys, zirconium and zirconium base alloys. Where such process is utilized in attempting to clean the strip of refractory metal, it is found that the metal immersion rolls which are utilized to maintain the strip immersed in the molten alkali metal caustic bath accumulate metal oxides which have been removed from the strip by the bath with the result that such metal oxides are picked up on the strip from such rolls and are carried thereby into a pickling tank which is usually positionedadjacent the caustic bath tank. It has been impossible heretofore to remove such oxides from the strip in the sulfuric and nitric hydrofluoric acids normally employed as pickling solutions with the result that imperfect strip material is obtained and a high rate of rejection is encountered.

An object of this invention is to provide apparatus for facilitating the removal of oxides from the surface of strip formed from refractory metal of the class of titanium, titanium base alloys, zirconium and zirconium base alloys.

Y Another object of. this invention is to provide apparatus .in conjunction with a molten "alkali caustic metal bath for maintaining a strip of refractory metal-immersed 'therein and effect a reaction between the caustic of the 'bath and the oxides and to effect the removal of the metal of such oxides from the caustic bath without detri- -mentally affecting the strip.

A further object of this invention is to provide for passing a strip of refractory metal through a molten alkali metal caustic bath to effect a reaction between the .caustic of the bath and the oxides on the surface of the --strip. to remove oxides therefrom and to rotate and continuously cool an idler roll in the bath out of contact :with'the strip to attractthe oxides so removed from the strip and thereby free the bath ofsuch. oxides without detrimentally affecting the strip.

Other objects of this invention will become apparent from the following description when taken in conjunction With the accompanying drawing in which: l ,1 Figure 1' is' a view in side elevation and partly 1n section of apparatus embodying features of this invention, and

Fig. 2 is a top plan view of a portion of the apparatus illustrated in Fig. 1.

Referring to the drawing, and in particular to Fig. .1 thereof, this invention is illustrated by reference to the immersion of a strip 10 of refractory metal of the class of titanium, titanium base alloys, zirconium and zirconium base alloys in a heated alkali metal caustic bath 12 usually having a sodium base and which is in a molten state, the caustic bath being contained in an iron-base tank 14. Associated with the tank 14 at the entrance end thereof is a roll 16 of asbestos or the like over which the strip 10 passes to enter the metal caustic bath 12, the roll 16 being supported in any suitable manner. As illustrated, a roll 18 formed of an iron-base metal and commonly termed an immersion roll is disposed adjacent the entrance end of the tank 14 with at least a portion of the roll 18 immersed in the caustic bath for holding the strip 10 immersed in the bath. The roll 18 may be of any suitable type and is preferably mounted with the ends of its shaft in suitable bearings (not shown) assembled in bearing housings 20 which are carried on the upper edges of the opposite sides of the tank 14.

In this embodiment a small hold-down roll 22 is disposed in spaced relation with respect to the immersion roll 18 being suitably mounted with the ends of its shaft in suitable bearings (not shown) mounted in bearing housings 24 on the tank 14 so as to effectively engage the strip 10 and maintain it immersed in the caustic bath for the distance between the roll 18 and a point closely adjacent the hold-down roll 22. Adjacent the exit end of the tank 14 there is disposed a wiper roll 26 formed of an iron-base metal which is also suitably mounted with the ends of its shaft in suitable bearings (not shown) mounted in bearing housings 28 carried on the upper edges of the opposite sides of the tank 14 for effecting a wiping of the strip 10 as it emerges from the caustic bath 12. In order to insure that the wiping roll 26 is clean, a cleaning brush 30 is disposed adjacent the wiping roll 26 and in contact therewith for efiectively removing any accumulation of dirt or the like from the wiping roll 26; the cleaning roll 30 is of the same length as the wiper roll 26 and is suitably. mounted with the ends of its shaft disposed in suitable housings 32 carried on the upper edges of the tank 14.

In accordance with this invention a pair of idler rolls 34 and 36 formed of an iron-base metal are disposed in spaced relation to one another between the immersion roll 18 and the hold-down roll 22, with at least the lower edges of the rolls 34 and 36 immersed in the caustic bath 12 contained in the tank 14 but out of contact with the strip 10 which passes therebelow. The rolls 34 and 36 are suitably supported in operative relation by having the ends of their shafts mounted in suitable bearings (not shown) supported in bearing housings 38 and 40, respectively, carried on the upper edges of the opposite sides of the tank 14. As illustrated in Fig. 2, each of the rolls 18, 26, 34 and 36 is connected as through suitable couplings 42, 44, 46 and 48, respectively, and gear reducers 50, 52, 54 and 56, respectively, to be driven by independent motors 58, 60, 62 and 64, respectively, the rolls 34 and 36 being usually driven at a slower rate of speed than the rolls 18 and 26 as will be explained more fully hereinafter. For purposes of clarity in showing the relative positioning of the different rolls, the strip 10 has been omitted from the showing made in Fig. 2.

In accordance with this invention one end of the shaft of each of the rolls 34 and 36 is suitably drilledand connected as by conduit 66 and 68, respectively, to a pipeline 70 for permitting the continuous admission of a suitable coolant to the interior of the rolls 34 and 36 throughout the operation of the apparatus. The op- 3 posite end of the shaft of each of the rolls 34 and 36 is also suitably drilled so as to provide an opening 72 and 74, respectively, which is connected to the interior of the associated roll for effecting the circulation of the air througheach of the rolls 34 and 36.

In practice the alkali metal caustic bath may be any of the' well known commercial salt baths which usually have'a sodium base and are preferably heated and maintained at temperature in the neighborhood of 875? F. to; 975 F. so that the salt bath is in a molten state and will readily react with the oxides normally contained on the surface of the strip 10 as the strip is admitted to the tank14 beneath the roll 18. .While many variations 111 11116 composition of the alkali metal caustic bath are p ossibleja typical example of a suitable caustic bath is that of the commercially known Virgo salt having about 8S.5-5%'so dium hydroxide, about 7.66% sodium nitrate, l'.72 'sodiiiin chloride and 0.53% sodium carbonate with traces of manganese dioxide present. The Kolene salts formed of alkali metal hydroxides, nitrates and chlorides as; described in Patent 2,458,661 are also effective for reacting with the oxides normally contained on thesuirfacje of the strip 10.

In utilizing the apparatus and practicing the process of thisinventionjthe strip 10 is admitted to the metal caustic bath 12 and passed beneath the immersion roll 18 and the hold-down roll 22 and emerges from the bath thereafter to, pass over the wiper roll 26 and from thence to apickling tank (not shown) containing a suitable pickling solution. As will be appreciated, with the temperature of the caustic bath 12 at from 875 F. to 975 F., the rolls 18 and 26 which are rotated with a portion thereof immersed. in the bath 12 soon attain substantially the temperature 'of the bath 12. These rolls are driven at a rate dependent pon the speed at which the strip 10 is passed through the bath 12 in the tank 14. Usually such rolls are driven at a speed in the neighborhood of 10 revolutionsiper minute.

In accordance with this invention a coolant such as air is supplied through the pipe .70. from a source (not shown) to provideacontinuous supply of cool air to the interior o f the idler rolls 34 and 36 .to effect a substantiallowering ofthiemperture of such rolls below the temperature dfthe ir'n'rnefrsiori. roll 1 8 andltheiwiper roll 26-,and the temperature of the .bath 12 in which the,lower edges of the iolls 34 and'36 are immersed. The rolls 34-an d 36 are preferably driven at a speed somewhat lower than the speed of the rolls 1 8 and 26 so a s to. permit adequate coolin g' of' the surface of the rolls 34 and 3 6 ;as they are ex sedtathe atmosphere to thereby continuously present'dooled surfacesifor immersion in thebath 12; In practicelthef rolls 34 and 36 are rotated at a speed in the neighborhood. of 2 to 3 revolutions per minute and the temperature a such rolls is preferably maintained at below 650 F. In actual practice it is foundthat the rol 1f36will be maintained at a substantially cooler tempefature than the roll 34, as a smaller portion thereof, as illustratedin Fig. 1, is maintained immersed in the caustic, bath 12. Usually the roll 36 will be found to have a temperaturefrorn to 75 cooler than the temperature of theroll 34 which in practice is preferably maintained at a temperature of not over 625 F.

As the; strip 19 enters the bath 12, the molten alkali metal caustic bath reactswith the oxides containedon the strip andcertain of the oxides gointo solution. in the bath. Prior to this invention since the rolls 18 and 26, whil being at substantially the temperature of the bath 12, are in effect cooler than the bath 12, they preferentially attracted the oxides in thebath with the, result that a buildup of such metal and oxides accumulated on the surface of such rolls and was picked up by the strip 10 during its contact with such rolls. Such deposits onthe rolls 18 and 26 when picked up therefrom by the strip 10,'caus edthe damage to the strip, it being found substantially impossible to remove such picked up metals and oxides from the strip in the pickling tank (not shown). It is to be noted that when analyzed the material accumulated or picked up by the cooled rolls where the strip being treated is a titanium base alloy comprised of from 55 to titanium dioxide and the balance caustic compounds.

With the rolls 34 and 36. being disposed as described hereinbefore and cooled to a temperature substantially lower than the temperature of the rolls 18 and 26, the oxides dissolved in the bath 12 from the strip 10 are no longer attracted to the warmer rolls 18 and 26, but instead are preferentially attracted by the cooler surfaces of the slowly rotating idler rolls 34 and 36 with the result that the pickup of such oxides from the bath 12 is substantially isolated to the idler rolls 34 and 36 which, while partially immersed in the bath, are out of contact with the strip 10. Thus since the oxides are removed from the bath 12 and deposited on the idler rolls 34 and 36, the rolls 18 and 26 are substantially free therefrom with the result that such oxides are no longer deposited on the rolls 18 and 26 and rolled into the strip 10' as the strip is contacted thereby and rejections by reason of such pickups on the strip 10 are minimized.

By providing for the preferential accumul'ati'onof the oxides on the rolls 34 and 36 it is no longer necessary to shut down the line to clean the submersion roll 18 or the wiper roll 26, as the idler rolls 34 and 36 can be readily removed from the assembly and replaced before any detrimental amounts of the oxides are deposited on the rolls 18 and 26 as the strip 10 passes through the bath. Prior to the development of the apparatus and method of this invention, in utilizing the standard equipment without theidler rolls 34 and 36, it was the general practiceto'have' to change the immersion roll 18, hold-down roll 22 and wiper roll'26 one to three times in a 24-hour period of operation. Theapparatus and method of this invention, however, has so improved operating conditions that only the idler rOlls 34-and 36 must now be changed and this only at approximately every 3 to'S days as opposed to the shorter intervals of the previous practice. With-the'idler rolls 34 and 36 present there is no necessity tochangeor clean the submersion; hold-down and wiper rolls, and as amatter of practice such rolls are only changedat very infrequent intervals of frorn'two to three months; In addition to effecting economies" through eliminating the frequent shutdowns'of the apparatus, the apparatus and method of, this inventi'on'have made it possible to Overcomethe disadvantages of .theprevious practice and to produce good clean strip material.

I claim:

l.- In apparatus, for removing oxides .from strip material formed from refractory metal selected from the class oftitanium, titanium =base alloys, zirconium and zirconium base alloys, the combination of, a tank adapted to contain a molten alkali metal ca-ustic'bath forreacting with the oxides on the strip, an immersion roll at least partially below the top of the tank and'adapted to be atleast partially immersed in said bath and in contact with the strip for 'holding the strip immersed therein, an idler roll partially below the top of the tank and adapted to .be at least partially immersed in said bath out of contact with the strip, means for efiecting rotation of the idler roll, and means for cooling the rotating idler roll to a temperature substantially less than the temperature of the immersion roll, the cooled idler roll cooperating in said bath to preferentially attract and receive metal oxides removed from the strip in said bath to thereby maintain the immersion roll substantially free from said metal oxides.

2. In apparatus for removing oxides from strip material formed from refractorymetal selected from "the class of titanium, titanium base' alloys, zirconium and zirconium base alloys, the combination of, a tank adapted to contain a molten alkali'metalcaustic bathfor reacting with'the oxides on-the stripyan'immersiorrroll at least partially below the top of the tank and adapted to be at least partially immersed in said bath and in contact with the strip for holding the strip immersed therein, a pair of idler rolls disposed in spaced relation to each other and partially below the top of the tank and adapted to be at least partially immersed in said bath out of contact with the strip, means for elfecting rotation of the idler rolls, and means for cooling each of the rotating idler rolls to a temperature substantially less than the temperature of the immersion roll, the cooled rotating idler rolls cooperating in said bath to preferentially attract and receive metal oxides removed from the strip in said bath to thereby maintain the immersion roll substantially free from said metal oxides.

3. In apparatus for removing oxides from strip material formed from refractory metal selected from the class of titanium, titanium base alloys, zirconium and zirconium base alloys, the combination of, a tank adapted to contain a molten alkali metal caustic bath for reacting with the oxides on the strip, a rotatable immersion roll at least partially below the top of the tank and adapted to be at least partially immersed in said bath and in contact with the strip for holding the strip immersed therein, means for effecting the rotation of the immersion roll, a rotatable idler roll partially below the top of the tank and adapted to be at least partially immersed in said bath out of contact with the strip, means for cooling the idler roll to a temperature substantially less than the temperature of the immersion roll, means for effecting the rotation of the idler roll at a speed substantially slower than the speed of the immersion roll but fast enough to present a cooled surface to the caustic bath, the cooled surface of the idler roll cooperating in said bath to preferentially attract and receive metal oxides removed from the strip in said bath to thereby maintain the immersion roll substantially free from said metal oxides.

4. In apparatus for removing oxides from strip material formed from refractory metal selected from the class of titanium, titanium base alloys, zirconium and zirconium base alloys, the combination of, a tank adapted to contain a molten alkali metal caustic bath for reacting with the oxides on the strip, a rotatable immersion roll at least partially below the top of the tank and adapted to be at least partially immersed in said bath for contacting and holding the strip immersed therein, means for effecting the rotation of the immersion roll, a pair of rotatable idler rolls disposed in spaced relation to each other and partially below the top of the tank and adapted to be at least partially immersed in said bath out of contact with the strip, means for cooling the idler rolls to a temperature substantially less than the temperature of the immersion roll, means for effecting the rotation of the idler rolls at a speed substantially slower than the speed of the immersion roll but fast enough to present cooled surfaces thereof for immersion in the caustic bath, the cooled surfaces of the idler rolls cooperating in said bath to preferentially attract and receive metal oxides removed from the strip in said bath to thereby maintain the immersion roll substantially free from said metal oxides.

5. In the method of removing oxides from strip material formed from refractory metal selected from the class of titanium, titanium base alloys, zirconium and zirconium base alloys, the steps comprising, passing the strip having oxides thereon into a molten alkali metal caustic bath, passing the strip beneath and in contact with at least one rotatable immersion roll partially immersed in the bath to maintain the strip in the bath and effect a reaction between the caustic and oxide on the strip and remove oxides therefrom, maintaining a rotatable idler roll partially immersed in the caustic bath but out of contact with the strip, rotating the idler roll, and cooling the rotating idler roll to maintain the rotating idler roll at a temperature substantially less than the temperature of the immersion roll whereby oxides removed from the strip in the caustic will preferentially be deposited on the cooled rotating idler roll to maintain the immersion roll substantially free from such oxides.

6. In the method of removing oxides from strip material formed from refractory metal selected from the class of titanium, titanium base alloys, zirconium and zirconium base alloys, the steps comprising, passing the strip having oxides thereon into a molten alkali metal caustic bath beneath at least one rotatable immersion roll at least partially immersed in the bath and in contact with the strip, the molten caustic bath reacting with oxides on the strip to remove oxides therefrom, rotating an idler roll at least partially immersed in the caustic bath but out of contact with the strip, and cooling the rotating idler roll to a temperature substantially less than the temperature of the immersion roll whereby the rotating idler roll continuously presents a cooled surface to the caustic bath, the continuously presented cooled surface functioning to preferentially attract the oxides removed from the strip in the caustic bath and maintain the immersion roll substantially free therefrom.

7. In the method of removing oxides from strip material formed from refractory metal selected from the class of titanium, titanium base alloys, zirconium and zirconium base alloys, the steps comprising, passing the strip having oxides thereon into a molten alkali metal caustic bath having a temperature of from 875 F. to 975 F., maintaining the strip immersed in the caustic bath by means of a rotating immersion roll in contact therewith, the immersion roll having a temperature developed therein closely approximating the temperature of the bath, the molten caustic bath reacting with oxides on the strip to remove metal in the form of oxides therefrom and form a compound insoluble in the bath, rotating an idler roll at least partially immersed in the caustic bath but out of contact with the strip, and cooling the rotating idler roll to a temperature of less than 650 F. to continuously present a cooled surface to the caustic bath, the cooled surface of the idler roll functi-oning to preferentially attract the insoluble compounds to maintain the immersion roll substantially free therefrom.

References Cited in the file of this patent UNITED STATES PATENTS 706,033 Davis Aug. 5, 1902 1,726,623 Hollnagel Sept. 3, 1929 2,674,550 Dunlevy et al. Apr. 6, 1954 

1. IN APPARATUS FOR REMOVING OXIDES FROM STRIP MATERIAL FORMED FROM REFRACTORY METAL SELECTED FROM THE CLASS OF TITANIUM, TITANIUM BASE ALLOYS, ZIRCONIUM AND ZIRCONIUM BASE ALLOYS, THE COMBINATION OF, A TANK ADAPTED TO CONTAIN A MOLTEN ALKALI METAL CAUSTIC BATH FOR REACTING WITH THE OXIDES ON THE STRIP, AN IMMERSION ROLL AT LEAST PARTIALLY BELOW THE TOP OF THE TANK AND ADAPTED TO BE AT LEAST PARTIALLY IMMERSED IN SAID BATH AND IN CONTACT WITH THE STRIP FOR HOLDING THE STRIP IMMERSED THEREIN, AN IDLER ROLL PARTIALLY BELOW THE TOP OF THE TANK AND ADPATED TO BE AT LEAST PARTIALLY IMMERSED IN SAID BATH OUT OF CONTACT WITH THE STRIP, MEANS FOR EFFECTING ROTATION OF THE IDLER ROLL, AND MEANS FOR COOLING THE ROTATING IDLER ROLL TO A TEMPERATURE SUBSTANTIALLY LESS THAN THE TEMPERATURE OF THE IMMERSION ROLL, THE COLLED IDLER ROLL COOPERATING IN SAID BATH TO PREFERENTIALLY ATTRACT AND RECEIVE METAL OXIDES REMOVED FROM THE STRIP IN SAID BATH TO THEREBY MAINTAIN THE IMMERSION ROLL SUBSTANTIALLY FREE FROM SAID METAL OXIDES. 